This proposal focuses on studies of epigenetic mechanisms of asthma during the period of adolescent transition, which encompasses hormonal and body mass index changes, growth effects, and the possible use of contraceptives, acetaminophen for relief of menstrual symptoms, and nicotine. Many studies have indicated a gender reversal of asthma prevalence during this transition due to a higher incidence and lower remission in girls. This provides a great opportunity to investigate the epigenetic mechanisms of asthma and associated risk factors during adolescence. Specifically, we will 1) assess genome-wide DNA methylation (DNA-M) at CpG sites using blood DNA samples taken before and after adolescent transition; identify CpGs associated with asthma transition and CpGs showing gender specificity in these associations; 2) test the association of asthma risk factors with DNA-M or its changes on these selected sites; 3) evaluate the agreement of methylation in peripheral blood leukocytes (PBL) and bronchial epithelial cells (BEC), and in PBL and in BEC, functionally assess the identified epigenetic marks in cis and trans via gene expressions and risk factors. Our overall hypothesis is: the reversal of asthma prevalence in adolescence can be explained by novel methylation difference between genders during the pre- to post-adolescent transition. We will test: (H1) DNA-M or its change across adolescence is associated with the change in asthma risk (TEMs), and the association is gender-specific (TGEMs). (H2) Adolescence-related, environmental, and socio-economic status (SES) risk factors are associated with DNA-M or its changes. (H3) DNA-M in PBL and BEC are correlated for CpG sites associated with asthma status. (H4) DNA-M of TEMs and TGEMs correlates with gene expression in PBL and in BEC and such correlation is gender specific, and (H5) gene expression is associated with TEMs and TGEMs- related risk factors. Expected findings will significant improve our understanding of gender-reversal of asthma prevalence in adolescence, thus provide a strong foundation for promoting asthma remission and predicting and preventing persistent and new onset asthma in adolescence. The results will help pediatricians and public health units to identify children at high risk of asthma in adolescence. Two comparable longitudinal birth cohorts will be investigated in this study. The Isle of Wight (IOW) birth cohort, established in 1989, is comprised of 1,456 children characterized for asthma and allergy at birth, 1, 2, 4, 10, and 18 years of age. The Avon Longitudinal Study of Parents and Children (ALSPAC) cohort in Bristol, established in 1991, includes 4,213 children characterized for asthma and allergy at ages 7-8 and 15-17 years. Both cohorts have extensive phenotype data, environmental exposure data, and DNA samples from pre- and post-adolescence. More importantly, PBL DNA-M have been measured for a large portion of subjects in each cohort. Our research team has a long track record of successful collaboration and two related projects [trans- generational epigenetic study 1R01AI091905, Karmaus (PI); asthma temporal phenotypic pattern study R21AI099367, Zhang (PI)] are recently funded by NIH.